Communication between a calling party (source) and a called party (destination) may be established over a communications network. Such a communications network may use source routed protocols in order to establish connections over which such communication can occur. Communication networks that support source routing protocols typically include a number of individual switches through which calls are routed. A call set-up message is sent along a path between the source and the destination through a number of intervening switches in order to establish the call. The path for the call set-up message to travel may be selected by the source in some networks or may be selected hop-by-hop by intervening switches in others.
Signaling protocols can encounter congestion in the control plane used to carry such set-up messages. The signaling plane congestion can be the result of a number of different factors, including an overabundance of signaling traffic such as call set-up messages and/or control plane datagram messages, device speed mismatches with the communication network, or over-utilization of particular nodes or switches within the network.
In some prior art systems, a node in the network under congestion may send a signaling congestion notification to the source node in response to a set-up message it received. In other prior art systems, it may simply drop the set-up message. Furthermore, even if the source node or any other nodes receive the notification, this action will not influence the routing of subsequent calls and so new calls will continue to be routed through the congestion point, only to block and be cranked back. As a result, sub-optimal use of network control plane resources occurs during periods of signaling congestion. This leads to call failures due to resource deficiencies and signaling protocol time-outs. In addition, it leads to large increase in call setup latency. Therefore, increased signaling congestion may result in severely degraded signaling performance.
In U.S. patent application Ser. No. 09/549,328, entitled “Method And Apparatus For Congestion Avoidance In Source Routed Signaling Protocol Communication Networks”, filed on Apr. 13, 2000 in the name of the present applicant, congestion avoidance techniques to prevent such a degradation of signaling performance are described. According to the techniques described therein, when control plane congestion is detected, a congestion notification message containing particulars of a congestion is generated and sent back to the source node or other nodes. A network element receives the congestion notification message and uses the particulars of a congestion for various network functions, including routing new set-up messages. Therefore, by understanding congestion information as it relates to the network topology, when generating a connection set-up message, a node can route the message in an intelligent manner that avoids congested portions of the network.
The present invention provides mechanisms that allow the network elements such as nodes to have knowledge of the state of signaling plane congestion, thereby allowing them to make more intelligent routing decisions, i.e., rate controlling call set up messages, routing control traffic around signaling congestion, regulating admission at the edge of the network.
The present invention is also applicable to routing and forwarding of connectionless traffic. The mechanisms of the present invention, therefore, also allow the network elements to have knowledge of the state of congestion in such plane, thereby allowing them to make more intelligent routing decisions.
The present invention works particularly well in conjunction with the techniques described in the above-referenced application. It should however noted that the present invention should also perform well in other environment, such as in the field of routing and forwarding any traffic, in which network elements are designed to react to congestion notification.